1. Field of the Invention
The invention relates to a signal processing apparatus and a method for processing signals, and particularly relates to an audio signal processing apparatus and a method for processing audio signals.
2. Description of Related Art
In a portable stereo system, loudspeakers usually share the same volume with each other to facilitate a low-frequency response. When the loudspeakers play different audio channels and share the same volume, they are easily affected by each other. Such phenomenon has a significant impact on the loudspeaker at the low-frequency. Specifically, clipping distortion may easily occur.
FIGS. 1 and 2 are respectively schematic views illustrating a shared-volume stereo system according to the conventional art. Referring to FIGS. 1 and 2, a shared-volume stereo system 100 includes a left channel loudspeaker 110 and a right channel loudspeaker 120. FIG. 1 is a schematic view illustrating cone excursions d1 of the left channel loudspeaker 110 and the right channel loudspeaker 120 when the left channel loudspeaker 110 and the right channel loudspeaker 120 are driven by low-frequency audio signals S1 and S2. In FIG. 1, the audio signals S1 and S2 are in-phase. Thus, when the left channel loudspeaker 110 and the right channel loudspeaker 120 are driven, the cone excursions thereof are in the same direction, such as toward inside or outside of the volume at the same time. Thus, the stereo system 100 may normally output a sound signal S3.
FIG. 2 is a schematic view illustrating cone excursions d2 of the left channel loudspeaker 110 and the right channel loudspeaker 120 when the left channel loudspeaker 110 and the right channel loudspeaker 120 are driven by the low-frequency audio signals S1 and S2. In FIG. 2, the audio signals S1 and S2 are out-of-phase. Thus, when the left channel loudspeaker 110 and the right channel loudspeaker 120 are driven, the cone excursions are not in the same direction. For example, the cone excursion of the left channel loudspeaker 110 is toward outside of the volume, while the cone excursion of the right channel loudspeaker 110 is toward inside of the volume. Thus, clipping distortion may occur in a sound output by the left channel loudspeaker 110 and the right channel loudspeakers 120. A waveform thereof is as shown by a sound signal S4. The waveform indicates that there is substantially no sound output from the stereo system 100. Namely, there are cone excursions both for the left channel loudspeaker 110 and the right channel loudspeaker 120, making the stereo system 100 unable to output a normal sound signal. Thus, how to avoid clipping distortion of the stereo system 100 and provide a preferable sound quality is certainly an important issue to work on.